Polychlorinated biphenyls (PCBs) and the DDT/DDE (DDE is the stored metabolite of DDT) family are toxic, widespread pollutants. Both pass from mother to child through the placenta and by contaminating breast milk. This project includes a study of subjects exposed to low levels of both compounds in North Carolina, a study in Mexico where levels of DDE are two to five times higher, and a study of children poisoned in utero by PCBs in Taiwan. In North Carolina, we reported that children who were exposed to the upper 5-10 percent of background PCB levels while in utero still had detectable motor delay at 18 and 24 months. We are following the children to see of delay persists. Using data from this project, we showed that the estimated cancer risk from chemicals in breast milk is mostly from PCBs, and that estimated excess mortality from this exposure is comparable to the estimated decrease in mortality from breast feeding. We have completed field work on a study in Mexico in which we look at lactation failure in women with high levels of DDE in milk, an observation we made previously in the US. In Taiwan, an epidemic of 2000 cases of PCB poisoning occurred in 1979. In 1985, we did a survey of 117 children who were born to mothers who were poisoned. We found developmental delay and physical abnormalities did not occur in the same children, and that children with more symptomatic mothers tended to have greater delay as follow-up progressed.